The present invention relates to the specific field of turbomachines and it relates more particularly to the problem posed by assembling a combustion chamber made of a composite material of the ceramic matrix composite (CMC) type in the metal casing of a turbomachine.
Conventionally, in a turbojet or a turboprop, the high pressure turbine, in particular its inlet nozzle (HPT nozzle), the combustion chamber, and the casing (or shell) of said chamber are all made out of the same material, generally a metal. Nevertheless, under certain particular conditions of use implementing particularly high combustion temperatures, a metal chamber turns out to be completely unsuitable from a thermal point of view and it is necessary to make use of a chamber that is based on high temperature composite materials of the CMC type. However, difficulties of implementation and materials costs mean that such materials are generally restricted to being used for the composite chamber itself, with the high pressure turbine inlet nozzle and the casing then still being made more conventionally out of metal materials. Unfortunately, metals and composites have coefficients of thermal expansion that are very different. This gives rise to particularly awkward problems of connection between the casing and the combustion chamber and of sealing at the nozzle at the inlet to the high pressure turbine.
The present invention mitigates those drawbacks by proposing a mounting for the combustion chamber in the casing with the ability to absorb the displacements induced by the various coefficients of expansion of those parts.
This object is achieved by a turbomachine comprising a shell of metal material containing in a gas flow direction F: a fuel injector assembly, a composite material combustion chamber having a longitudinal axis, and a metal nozzle forming the fixed blade inlet stage of a high pressure turbine, wherein said composite material combustion chamber is held in position inside said metal shell by a plurality of flexible metal tabs having first and second ends, said first ends being interconnected by a flange-forming metal ring fixed to said metal shell by first fixing means, and each of said second ends being fixed by second fixing means both to said composite material combustion chamber and to one end of a composite material wall whose other end forms a bearing plane for a sealing element secured to said nozzle and providing sealing for the stream of gas between said combustion chamber and said nozzle, the flexibility of said metal fixing tabs allowing expansion to take place freely in a radial direction at high temperatures between said composite material combustion chamber and said metal shell.
With this particular structure for the fixed connection, the various kinds of wear due to contact corrosion in prior art systems can be avoided. The use of a wall made of composite material placed in line with the combustion chamber to provide sealing of the stream also makes it possible to reconstitute the initial structure of the chamber. In addition, the presence of flexible metal tabs replacing the traditional flanges gives rise to a saving in mass that is particularly appreciable. In addition to being flexible, these tabs make it easy to accommodate the expansion difference that appears at high temperatures between metal parts and composite parts (by accommodating the displacements due to expansion) while still ensuring that the combustion chamber is properly held and well centered in the shell.
The first and second fixing means are preferably constituted by a plurality of bolts. Nevertheless, the second fixing means could also be constituted by crimping elements. Advantageously, said sealing element is of the circular xe2x80x9cspring bladexe2x80x9d gasket type. It can have a plurality of calibrated leakage orifices.
In an advantageous embodiment in which the metal shell is made up of two portions, said metal ring interconnecting said first ends of said flexible metal tabs is mounted between connecting flanges of said two portions. In an alternative embodiment, said metal ring can be fixed directly to said annular shell by conventional fixing means.
Depending on the intended embodiment, said first ends of the fixing tabs can either be fixed by brazing (or welding) to said flange-forming metal ring, or else they can be formed integrally with said metal ring.